The electrochemical coreduction of carbon dioxide (CO 2 ) and nitrogenous species (such as NO 3 − , NO 2 − , N 2 , and NO) for urea synthesis under ambient conditions provides a promising solution to realize carbon/nitrogen neutrality and mitigate environmental pollution. Although an increasing number of studies have made some breakthroughs in electrochemical urea synthesis, the unsatisfactory Faradaic efficiency, low urea yield rate, and ambiguous C−N coupling reaction mechanisms remain the major obstacles to its large-scale applications. In this review, we present the recent progress on electrochemical urea synthesis based on CO 2 and nitrogenous species in aqueous solutions under ambient conditions, providing useful guidance and discussion on the rational design of metal nanocatalyst, the understanding of the C−N coupling reaction mechanism, and existing challenges and prospects for electrochemical urea synthesis. We hope that this review can stimulate more insights and inspiration toward the development of electrocatalytic urea synthesis technology.

Herein, a colorimetric detection strategy for alkaline phosphatase (ALP) activity was established based on an Fe-doped carbon-based nanozyme. By doping Fe into a Zn MOF and introducing dicyandiamide for pyrolysis, we obtained a twodimensional carbon nanosheet with exceptional peroxidasemimicking activity (Fe/C NS). The Fe/C NS has superior affinity to H 2 O 2 , can decompose H 2 O 2 into reactive oxygen species, and further oxidize reducing substances such as phenol. ALP can hydrolyze disodium phenyl phosphate into phenol, while the Fe/C NS can promote the reaction between phenol and 4-aminoantipyrine in the presence of H 2 O 2 to produce red quinone imine. Based on the changes of absorbance of the reaction system, ALP activity can be detected in a range of 0.05−6.00 U•L −1 with a detection limit of 0.03 U•L −1 . Furthermore, we developed a quantitative relationship between ALP activity and color characteristic values by recording the RGB (red, green, and blue) values of color changes under different ALP concentrations, realizing the convenient determination of ALP activity without specific analytical equipment. This work can effectively broaden the application of nanozymes in biological analysis.

Herein, lysozyme-functionalized 5-methyl-2-thiouracil gold/silver nanoclusters (5-MTU/Lys Au/Ag NCs) with an orange-red fluorescence peak at 600 nm (quantum yield = 33.18%) were obtained through a simple blending route. Owing to the synergistic effect between Au and Ag and the formation of rigid host–guest assemblies between 5-MTU and the guanidine group of lysozymes, the chemical properties of 5-MTU/Lys Au/Ag NCs were significantly improved. Taking advantage of the exceptional optical properties and satisfactory stability of 5-MTU/Lys Au/Ag NCs, a fresh and sensitive fluorescent probe for monitoring alkaline phosphatase (ALP) was strategically constructed by the integration of 5-MTU/Lys Au/Ag NCs and the nanozyme with a graphene structure (Fe-G nanozyme) for the first time. Briefly, the fluorescence of 5-MTU/Lys Au/Ag NCs was initially quenched by indigo carmine (IC) through the inner filter effect (IFE) mechanism, but it was restored upon the introduction of H2O2 and Fe-G nanozyme by generating reactive oxygen species (ROS) (1O2/O2 •–) and promoting the oxidative degradation of IC, whereas the fluorescence was quenched again in the presence of ALP via hydrolyzing l-ascorbic acid-2-phosphate (AAP). By monitoring the changes in signal intensity, the proposed fluorescent sensing platform presented a highly selective and excellent performance toward ALP, exhibiting a good linear relationship from 0.5 to 10 U L–1 and providing a low detection limit of 0.193 U L–1. Furthermore, the proposed biosensor showed satisfactory results for quantifying ALP in human serum.